Semiconductor device package having features formed by stamping

ABSTRACT

Embodiments of the present invention relate to the use of stamping to form features on a lead frame of a semiconductor device package. In one embodiment, portions of the lead frame such as pins are moved out of the horizontal plane of a diepad by stamping. In certain embodiments, indentations or a complex cross-sectional profile, such as chamfered, may be imparted to portions of the pins and/or diepad by stamping. The complexity offered by such a stamped cross-sectional profile serves to enhance mechanical interlocking of the lead frame within the plastic molding of the package body. Other techniques such as selective electroplating and/or formation of a brown oxide guard band to limit spreading of adhesive material during die attach, may be employed alone or in combination to facilitate fabrication of a package having such stamped features.

CROSS-REFERENCE TO RELATED APPLICATION

The instant nonprovisional patent application claims priority to U.S.Provisional Patent Application No. 61/042,602 filed Apr. 4, 2008 andincorporated by reference in its entirety herein for all purposes.

BACKGROUND OF THE INVENTION

FIGS. 1A-1H show simplified cross-sectional views of a conventionalprocess for fabricating a package for a semiconductor device. The viewsof FIGS. 1A-H are simplified in that the relative proportions of thevarious components are not shown to scale.

In FIG. 1A, a planar, continuous rolls 102 of conducting material suchas copper, is provided.

In FIG. 1B, material is removed from regions of the planar roll 102utilizing a chemical etching process. This chemical etching processinvolves forming a mask, and then etching in regions exposed by themask, followed by removal of the mask. This chemical etching serves todefine a central diepad 104 surrounded by a metal matrix 106. Althoughnot shown in the particular cross-sectional view in FIG. 1B, portions ofthe diepad 104 may remain integral with the metal matrix 106.

FIG. 1C shows partial etching of the backside of portions of thepatterned roll 102. Etched regions 104 a of the periphery of the diepad104 will later serve to allow the diepad to be physically secured withinthe plastic molding of the package body. Etched regions 108 a correspondto portions of pins of the lead frame. These etched regions 108 a willlater serve to allow the pins to be physically secured within theplastic molding of the package body. FIG. 1C marks the step ofcompletion of formation of lead frame 103.

FIG. 1D shows the formation of an electrically conducting adhesivematerial 110 on the die attach region 104 b of the diepad 104. Thiselectrically conducting adhesive material may comprise soft solderdeposited in molten form. Alternatively, the electrically conductingadhesive material may comprise solder paste that is deposited in theform of small-sized particles of solder in a binder such as a solvent.

FIG. 1E shows the die-attach step, wherein the back side 112 a ofsemiconductor die 112 is placed against electrically conducting adhesivematerial 110. As shown in FIG. 1E, one consequence of this die attachstep may be the spreading of material 110 on the diepad 104 beyond theperimeter of the die 112.

FIG. 1F shows a subsequent step, wherein bond wires 114 are attachedbetween contacts on the top surface 112 b of the die 112 and pins 108.

FIG. 1G shows a further subsequent step, wherein the diepad 104, die112, bond wires 114, and portions of the pins 108 are encapsulated witha plastic molding material 116 to define a body 118 of the package. Aspreviously indicated, the recesses 104 a and 108 a serve to physicallysecure the diepad and pins, respectively, within the package during thisencapsulation step.

FIG. 1H shows a subsequent singulation step, wherein the package 120 isseparated from the surrounding metal frame by a sawing process.

While the conventional process flow just described is adequate to form asemiconductor device package, it may offer certain drawbacks. Inparticular, the partial etching step shown in FIG. 1C may be difficultto achieve, and hence adds to the cost of manufacturing the device. Inparticular, this partial etching step involves a number of steps,including the highly accurate patterning of a mask, followed by onlypartial etching in exposed areas and then removal of the mask. Inparticular, the partial etching of the metal roll may be difficult tohalt with sufficient accuracy and repeatability.

Accordingly, there is a need in the art for a process for forming asemiconductor device package which avoids the need for a partial etchingstep.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention relate to the use of stamping toform features on a lead frame of a semiconductor device package. In oneembodiment, portions of the lead frame such as pins are moved out of thehorizontal plane of a diepad by stamping. In certain embodiments, acomplex cross-sectional profile, such as chamfered, may be imparted toportions of the pins and/or diepad by stamping. The complexity offeredby such a stamped cross-sectional profile serves to enhance mechanicalinterlocking of the lead frame within the plastic molding of the packagebody. Other techniques such as selective electroplating and/or formationof a brown oxide guard band to limit spreading of adhesive materialduring die attach, may be employed alone or in combination to facilitatefabrication of a package having such stamped features.

These and other embodiments of the present invention, as well as itsfeatures and some potential advantages are described in more detail inconjunction with the text below and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-H show simplified cross-sectional views of a conventionalprocess for fabricating a package.

FIGS. 2A-2K show simplified cross-sectional views of an embodiment of aprocess in accordance with the present invention for forming a package.

FIGS. 2CA-2CC show end views of various complex cross-sectional profilesthat may be imparted by stamping according to embodiments of the presentinvention.

FIG. 3 shows a simplified view of the flow of a process according to anembodiment of the present invention.

FIG. 4A shows a simplified perspective view of the lead frame of anembodiment of a package in accordance with the present invention housingthree die.

FIG. 4B is a simplified plan view showing the die and bond structures ofthe package of FIG. 4A.

FIG. 5 is a simplified plan view showing a lead frame according toanother embodiment of the present invention.

FIG. 5A is a simplified cross-sectional view taken along the line A-A′of FIG. 5.

FIG. 5B is a simplified plan view showing positioning of a die and bondwires on the lead frame of FIG. 5.

FIG. 6 is a simplified plan view showing a lead frame according to yetanother embodiment of the present invention.

FIG. 6A is a simplified cross-sectional view taken along the line A-A′of FIG. 6.

FIG. 7A is a simplified cross-sectional view of another embodiment of alead frame of the present invention.

FIG. 7B shows an enlarged plan view of a portion of the lead frame ofFIG. 7A.

FIG. 7C shows an enlarged cross-sectional view of the lead frame of FIG.7B taken along line C-C′.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention relate to the formation ofsemiconductor device packages utilizing stamping. In one embodiment,portions of the lead frame such as pins are moved out of the horizontalplane of a diepad by stamping. In certain embodiments, the pins of apackage may be imbued with a chamfered or other complex cross-sectionalprofile by a stamping process. Other techniques, employed alone or incombination, may facilitate fabrication of a package by stamping.

FIGS. 2A-2K show simplified cross-sectional views of a process inaccordance with an embodiment of the present invention for forming asemiconductor device package. The views of FIGS. 2A-2K are simplified inthat the relative proportions of the components of the package are notshown to scale.

In FIG. 2A, a planar, continuous roll 202 of conducting material such ascopper, is provided. In particular embodiments, the metal roll may havea thickness of between about 4-20 mils (0.004″-0.020″). In certainembodiments, the metal roll has a thickness of between about 6-10 mils(0.006″-0.010″).

In FIG. 2B, material is removed from the planar roll 202 utilizing apunching process, with points of removal of material indicated by thetriangles. This punching process serves to define a central diepad 204surrounded by a metal matrix 206. Although not shown in the particularcross-sectional view in FIG. 2B, portions of the diepad 204 may remainintegral with the surrounding metal matrix 206.

Also defined during the punching step of FIG. 2B are a plurality of pins208 integral with the surrounding metal matrix. According to certainembodiments, the minimum width of these pins is about 0.15 mm, and theminimum pitch between the pins is about 0.4 mm, where the pitch isdefined as the distance between the center lines of adjacent pins. Inparticular embodiments where the thickness of the metal roll is betweenabout 6-10 mils, the width of these pins is about 0.25 mm and the pitchbetween the pins is about 0.5 mm.

FIG. 2B shows that the lateral dimension (A′) of the diepad 204, may beslightly smaller than the corresponding lateral dimension (A) of thediepad 104 formed by the conventional process shown in FIG. 1B. Asdiscussed in detail below, this smaller diepad size may be a result offabrication of the package utilizing stamping techniques.

Specifically, FIG. 2C shows the use of stamping to impart severalfeatures to the lead frame. One feature formed by stamping is anindentation at the edge of the diepad and/or pins. Specifically, FIG. 2Cshows indentation 204 a around the periphery of the underside of diepad204. FIG. 2C also shows indentation 208 a at the edge of the pin.proximate to the diepad. By receiving the plastic molding of the packagebody during the subsequent encapsulation step, stamped indentations 204a and 208 a serve to enhance mechanical interlocking between the body ofthe package and the diepad and pins respectively.

Another lead frame feature shown in FIG. 2C formed by stamping, iselevation of a portion 208 b of pins 208 above a horizontal plane of thediepad 204. This raising of portions 208 b of the pins 208 closest tothe diepad 204, causes the pins to penetrate deeper into the body of thepackage, helping to physically secure the pins within the encapsulatingplastic mold of the package body. Raising of the pin portions alsorelieves stress in the bond structure, by making the ends of the bondstructure located at approximately the same height.

According to certain embodiments, the stamping process may raise the pinportions 208 a to a height Z above the surface of the diepad 204, whereZ corresponds approximately to an expected thickness of a die supportedon the diepad, and a conducting adhesive material between the die andthe diepad.

Still another feature which may be imparted to a lead frame during thestamping of FIG. 2C, is a complex cross-sectional profile to a middleportion 208 c of the pin 208. Specifically, FIG. 2CA shows a view ofmiddle portion 208 b of the pin 208, taken along section A-A′ of FIG.2C. FIG. 2CB shows a view of a portion of the pin 208 taken alongsection B-B of FIG. 2C.

In the particular embodiment of FIGS. 2CA-CB, the middle pin portion 208b exhibits a chamfered profile, with sides positioned at an anglerelative to the vertical disposition of the sides of the other portionsof the pin. In this embodiment, the complex cross-sectional profilesimparted to the lead frame by stamping according to embodiments of thepresent invention, enhances mechanical interlocking of the pins withinthe plastic body of the package. In addition, the stamped cross-sectionsallow the pins to offer a larger surface area to the surrounding moldingmaterial, thereby further enhancing mechanical interlocking between leadframe and package body. Moreover, the complex stamped cross-sectionalprofiles may allow the pins to better relieve physical stress during thesubsequent singulation step, thus avoiding damage at the interfacebetween the pin and the plastic package body.

While FIG. 2CA shows the complex cross-sectional profile as being achamfer, this is not required by the present invention. In otherembodiments, the cross-sectional profile imparted by stamping could behour-glass shaped, T-shaped, H-shaped, angled or curved concave orconvex, or saw tooth shaped, as shown in FIG. 2CC.

The various features formed by stamping in FIG. 2C need not be createdin a single stamping step. One or more separate stamping impacts underdifferent conditions could be employed to create the stamped features.

FIG. 2D shows a simplified view of a post-stamping electroplatingprocess according to an embodiment of the present invention.Specifically, electroplated material 222 is selectively formed oncertain regions of the lead frame.

Specifically, electroplated material 222 may be formed on the die attachportion 204 b of the diepad 204 that is expected to receive the die.Where the die to be supported by the diepad has an electrical contact onits lower surface (such as the drain of a MOSFET), the electroplatedmaterial 222 will likely contain silver (Ag).

Another location of electroplated material is at an end of the elevatedportion 208 a of the pin 208 proximate to the diepad 204. As discussedin detail below, these electroplated regions are expected to receive theelectrically conducting bond wire, bond ribbon, or bond clip from thetop surface of the supported die.

The composition of the electroplated material 222 may be dictated by thecomposition of the bond wire/ribbon/clip with which the electroplatedmaterial will be in contact. The following TABLE provides a listing ofelectroplated materials under different conditions.

TABLE Bonding Material Finished Lead Surface for Bonding Wire Gold WireNi, Ag, Ni/Au, or Ni/Pd/Au Al-Wire Bare Cu, Ni, Ag, Ni/Au, or Ni/Pd/AuCu-wire Bare Cu, Ni, Ni/Au, or Ni/Pd/Au Ribbon Al Bare Cu, Ni, Ag,Ni/Au, or Ni/Pd/Au Cu- Bare Cu, Ni, Ni/Au, or Ni/Pd/Au Clip Cu Bare Cu,Ni, Ni/Au, or Ni/Pd/Au

FIG. 2E shows a next step in the process, wherein the electroplated leadframe is exposed to an oxidizing ambient 224. As a result of thisexposure, portions of the lead frame that have not been electroplated,become oxidized and form “brown oxide” 226. As discussed below, thisbrown oxide 226 may exhibit properties that are useful in subsequentsteps in the package. In particular, formation of a brown oxide guardband 226 a circumscribing the die attach area 204 b, may be useful.

FIG. 2F shows the next step, wherein die 212 is provided having itslower surface 212 a already coated with an electrically conductingadhesive material 210 such as soft solder. This step obviates the needfor the selective deposition of the electrically conducting adhesivematerial on the die attach area that is shown in FIG. 1D of theconvention process.

FIG. 2G shows the next step, wherein die 212 bearing electricallyconducting adhesive material 210, is placed against die attach area 204b of diepad 204. In this step, the presence of the brown oxide guardband 226 a secures to restrain the flow of the soft solder materialbeyond the confines of the die attach area. Specifically, the roughnessand non-wetting properties of the brown oxide inhibit the spreading ofthe soft solder. The thickness of the die 212 supported on the diepad204 and a conducting adhesive material 210 between the die and thediepad corresponds approximately to a height Z above the surface of thediepad 206 a, as shown in FIG. 2H and discussed above.

FIG. 2I shows the next step, wherein the appropriate bonding structures214 are attached between the surface of the die 212 b and theelectroplated material 222 of an appropriate pin 208. As discussed abovethe bond structure may be a conducting clip, wire, or ribbon.

FIG. 2J shows a step in which the die 212, bonding structures 214, andportions of the pins 208 and diepad 204 are encapsulated within aplastic molding material 228 to form the body of the package 220. Duringthis step, the diepad and pins remain fixed to the surrounding metalmatrix of the original metal roll.

During the package singulation process shown in FIG. 2K, the pins 208are exposed to significant physical strain as the punching blade movesthrough the metal. However, during this slicing process the angled edgesoffered by the chamfered cross-sectional profile of the pin shown inFIG. 2CA, serves to enhance mechanical interlocking of the pins withinthe plastic body material, and reduce physical strain at the interfacebetween the pins and the package body.

The package singulation process in FIG. 2K leaves package 220 havingexposed surface 208 d of pin portions 208 and exposed surface 204 d ofdiepad 204 stripped of brown oxide and ready for soldering to anunderlying printed circuit (PC) board (not shown).

While the particular embodiment shown above depicts fabrication of apackage housing a single die, the present invention is not limited tosuch a package. Alternative embodiments in accordance with the presentinvention could be used to form packages housing two, three, or evenlarger numbers of die.

FIG. 3 shows a simplified flow diagram of a process for fabricating apackage according to an embodiment of the present invention. In a firststep 302 of process 300, a continuous planar roll of conducting materialis provided.

In a second step 304 of process 300, holes are punched completelythrough to remove material from the metal role and thereby define thepattern of the diepad and pins.

In a third step 306, the patterned metal roll is subjected to one ormore stamping processes to create features on the pin and diepadportions of the package. As discussed in detail above, examples of suchfeatures include indentations on the underside of the diepad, pinportions exhibiting a chamfered cross-sectional profile, and raised pinportions.

In a fourth step 308, portions of the lead frame may optionally beelectroplated with an appropriate metal. Examples of such electroplatedregions include the die attach area, and the raised portions of the pinsthat are expected to receive an end of a bond structure such as a wire,ribbon, or clip having its other end in contact with the die.

In a fifth step 310, the stamped lead frame is exposed to an oxidizingambient. A result of this exposure to the oxidizing ambient is theformation of brown oxide on all exposed portions of the lead framesurface. As discussed previously, this oxidation may desirably lead tothe formation of an oxide guard band circumscribing the die attach area.

In a sixth step 312, brown oxide on the bottom surface of the pins anddiepad may be removed. In certain embodiments, this oxide removal may beaccomplished by physically lapping the bottom of the lead frame. Inother embodiments, this oxide removal may be accomplished by exposure toa chemical etching environment.

The oxide removal step may occur immediately following the oxidationstep, as indicated in FIG. 3. In other embodiments, however, the oxideremoval step may occur later in the process, for example following theencapsulation step.

In a seventh step 314, the die is attached to the die attach area. Incertain embodiments, this die attach step may include prior applicationof an electrically conducting adhesive material to the die attach areaof the diepad. Alternative embodiments may utilize a die having its backside already coated with the electrically conducting adhesive material.

In an eighth step 316, the appropriate bonding structure(s) are attachedbetween the surface of the die and the appropriate pin, which may beelectroplated. As discussed above, the bond structure may be aconducting clip, wire, or ribbon. See, for example, FIG. 2I.

In a ninth step 318, the die, bond structure, and portions of the pinsand diepad are encapsulated within a plastic molding material to formthe body of the package. During this step, the diepad and pins remainfixed to the surrounding metal matrix of the original metal roll. See,for example, FIG. 2J.

In a tenth step 320, the individual package is singulated from thesurrounding metal matrix by punching through the metal. During thissingulation process, a chamfered or other complex cross-sectionalprofile imparted to the pins by stamping, may enhance mechanicalinterlocking of the pins within the package body, and allow the pins torelieve physical stress resulting from the shearing of the metal.

In additional steps (not shown), the package may be attached to anunderlying PC board utilizing solder. The previous removal of brownoxide by lapping may facilitate the performance of this step.

The process described above represents only one particular embodiment ofthe present invention. Other embodiments may omit certain steps, includeadditional steps, or perform the steps in a specific order other thanthat indicated.

For example, the selective electroplating step is not required, andaccording to certain embodiments the bonding structure may be in contactwith the bare metal of the roll rather than an electroplated feature.Moreover, the use of a bonding clip is not required by the presentinvention and certain embodiments could employ only bonding ribbons orwires to establish electrical connection with contact(s) on the top ofthe die.

Embodiments in accordance with the present invention offer a number ofpossible advantages over conventional package fabrication processes. Inparticular, by avoiding the need for complex and difficult-to-achievesteps of forming raised/recessed features on the lead frame by markingand partial etching, embodiments in accordance with the presentinvention offer cost savings.

Comparison of FIGS. 1B and 2B indicates that one characteristic that maynot be offered by embodiments of the present invention, is a largerdiepad area available to support a larger die. Specifically, features onthe lead frame are formed by stamping that does not completely removethe material of the metal roll. Thus, in order to maintain the samelateral spacing B between the diepad and pins as in the etched package,embodiments of the present invention may utilize a diepad havingslightly reduced dimensions (A′ vs. A) in order to accommodate thestamped metal.

However, various other aspects of processes according to embodiments ofthe present invention may serve to offset any smaller size of the diepadand die. For example, the formation of the brown oxide guard bandcircumscribing the die attach area, effectively constrains the flow ofthe electrically conducting adhesive material during the die attachprocess. This in turn allows reduction in the peripheral area of thediepad that must be allocated to avoid the flowed material fromundesirably affecting regions outside the die attach area.

Moreover, certain embodiments involve the use of clips instead of bondwires. Such use of a bond clip may allow for a reduced resistanceelectrical connection between the die contacts and the surrounding pins.This may in turn permit the use of a smaller die having performancecomparable to a larger one.

Similarly, the use of selective electroplating may also offer a reducedresistance electrical connection between the die contacts and thesurrounding pins. Again, this offers the possibility of a smaller dieexhibiting performance comparable to a larger die.

The above figures present an exemplary embodiment only, and the presentinvention is not limited by this particular embodiment. For example,while the above figures show a diepad having indented features formed bystamping, this is not required by the present invention. According toother embodiments, a diepad could have raised features formed bystamping, such as raised features on a periphery of the diepad.

Moreover, while the specific embodiment shown above includes pinportions proximate to the diepad that are elevated by stamping, thepresent invention is not limited to this approach. In accordance withalternative embodiments, portions of the pins distal from the diepadcould be inclined downward by stamping, thereby offering an embodimentwherein the bottom of the diepad is not exposed following encapsulationof the package body.

In addition, while the above figures describe an embodiment of a packageconfigured to house a single die, this is not required by the presentinvention. Alternative embodiments of packages according to the presentinvention can be configured to house two or more die.

For example, FIGS. 4A-B show different views of an embodiment of a quadflat no-lead (QFN) package housing three different die. Specifically,FIG. 4A shows a perspective view of the lead frame 403 only of the QFNpackage. FIG. 4B shows a plan view of the entire package 420 of FIG. 4A,including the die housed therein and the bonding structures attachedthereto, with the outline of the plastic package body shown.

The lead frame 403 of the particular embodiment of FIGS. 4A-4B is formedfrom a copper roll having a thickness of between about 6-10 mils. Thepins 408 have a width of about 0.25 mm or greater. The pitch between thepins is about 0.5 mm or greater.

Specifically, the stamped end frame 403 of package 420 comprises threediepads 404, 407, and 409, respectively supporting first MOSFET die 412,second MOSFET die 455, and integrated circuit (IC) die 460. Diepad 404is the largest of the three, having an elongated die attach area 404 aconfigured to support MOSFET die 412.

The pins of the package offer contact with three discrete portions ofthe first MOSFET die 412. Specifically, ganged pin nos. 21-27 are in lowresistance communication with the source contact located on the topsurface of the die 412, through clips 450. Pins 16, 20, and 28-31 areintegral with the diepad 404, and hence offer a low resistanceelectrical communication with the drain of the MOSFET through a contactin the bottom surface of the die. The gate of the MOSFET is inelectrical communication with a contact of the integrated circuit (IC)die 409 through bond wire 452.

Similarly, the pins of the package 420 offer contact with three discreteportions of the second MOSFET die 455. Specifically, ganged pin nos.34-36 are in low resistance communication with the source contactlocated on the top surface of the die 455, through bonding clips 450.Pins 1-2, 4, and 33 are integral with the diepad 407, and hence offer alow resistance electrical communication with the drain of the MOSFETthrough a contact in the bottom surface of the die. The gate of theMOSFET is in electrical communication with pin 3 through bond wire 452.

Unlike the MOSFET die just described, the IC die 460 features a largenumber of contacts on its top surface. These various contacts are inelectrical communication with the following pin nos.: 5, 7-9, 11-13, 15,and 17-18.

IC die 460 may or may not have an electrical contact in its lowersurface. If it does, pins 6, 10, and 14 integral with the diepad 409provide for low electrical resistance communication with that undersidecontact.

The multi-die embodiment of the QFN package 420 of FIGS. 4A-4B includesthe stamped features of the single die package. Specifically, thediepads include indentations 404 a, 407 a, and 409 a respectively asshown in dashed lines. These indentations are formed by stamping, andhelp to provide mechanical interlocking of the diepads with theencapsulant of the plastic mold material.

Another feature of the multi-die embodiment of the QFN package 420 ofFIGS. 4A-4B is the chamfered cross-sectional profile 408 c of portionsof the pins 408 lying just inside the plastic package body. As describedabove, these chamfered cross-sectional profile serves to enhancemechanical interlocking with the surrounding molding of the packagebody, and increase the amount of surface area of the pin in contact withthe plastic molding. In addition, the angled orientation of the sides ofthe pins serves to reduce stress within the package during punching atthe time of singulation.

Yet another feature of the multi-die embodiment of the QFN package 420of FIGS. 4A-4B is the raising of portions of the pins above thehorizontal plane of the diepad. Specifically, during fabricationportions of the pins are bent by stamping to impart them with aninclined portion 408 a and a corresponding raised portion 408 bproximate to the diepads. As previously indicated, such a profile helpsto ensure that the pins remain securely embedded within the plasticmolding of the package. The raised pin profile also serves to easestrain in the bonding structure, by placing the surface of the pin atthe height of the top surface of the die expected to be supported by thediepad.

As previously indicated, the multi-die embodiment of the QFN package 420includes an IC die which may or may not have an electrical contact onits back side. Such an IC die would not be expected to generate as muchheat as other dies such as MOSFETs. Accordingly, an epoxy die attachfilm may be used to adhere the IC die to the diepad. Such an epoxy filmmay be formed as a solid, and would not be expected to flow or spreadduring the die attach step. Accordingly, for embodiments of the presentinvention where a package is fabricated housing only an IC die,formation of a brown oxide guard band followed by lapping, may not benecessary.

While the embodiments described above illustrate the use of stamping toimpart a chamfered cross-sectional profile to pin portions, thisparticular cross-sectional profile is not required by embodiments of thepresent invention. According to alternative embodiments, stamping couldimbue pins with other cross-sectional profiles and remain with the scopeof the invention. Examples of such other cross-sectional profilesinclude but are not limited to hourglass shaped, angled or curvedconcave, angled or curved convex, or saw tooth.

During conventional package fabrication processes, the diepad may besecured to the surrounding metal of the roll utilizing tie-barstructures. These conventional tie-bar structures stabilize the diepadduring die attach, and encapsulation steps, and are then severed duringthe package singulation.

One advantage of embodiments in accordance with the present invention,is the dispensing of the need for a tie-bar structure. Specifically, theembodiment of FIGS. 4A-B does not include tie-bars or severed portionsthereof. In particular, prior to the singulation step, each diepad isconnected to a surrounding metal frame by way of at least twonon-integral pins that would be integral with surrounding portions ofthe metal matrix. These integral pin portions function in the role of atie-bar, physically stabilizing the diepad and insuring the physicalintegrity of the lead frame prior to the singulation step.

The absence of tie-bars offer a number of advantages. One advantage ishaving more area in the corners of a package to place more pins. Anotheradvantage is that there is no exposed part of tie bars on a surface of apackage.

While the embodiment of FIG. 4B shows a lead frame lacking tie-bars andincluding ganged groups of non-integral pins for communicating withnon-IC die, this is not required by the present invention. FIG. 5 is asimplified plan view showing a lead frame according to anotherembodiment of the present invention, and FIG. 5A is a simplifiedcross-sectional view taken along the line A-A′ of FIG. 5.

The embodiment of FIGS. 5-5A shows a lead frame 500 having tie-bars 502integral at the corners of the diepad 506. Coined indents 508 located onthe underside of the diepad 506 are configured to interlock with plasticmolding of the package upon encapsulation.

FIG. 5B is a simplified plan view showing positioning of a die and bondwires on the lead frame of FIG. 5. As shown in FIG. 5B, the large numberof exclusively single individual pins 510 of this embodiment, aresuitable for communicating through bond wires with the plurality ofcontacts present on a top surface of a complex IC die such as amicroprocessor, that is supported on the diepad.

Types of features other than those explicitly described above, can beformed on a lead frame by coining according to alternative embodimentsof the present invention. For example, FIG. 6 is a simplified plan viewshowing a lead frame according to yet another embodiment of the presentinvention, supporting a die. FIG. 6A is a simplified cross-sectionalview taken along the line A-A′ of FIG. 6, absent the die.

The embodiment of FIGS. 6-6A shows a lead frame 600 which includes anumber of holes 602 formed by stamping or coining, in the periphery ofthe diepad region 604. The holes 602 allow penetration of plasticmolding during the encapsulation step, thereby providing additionalmechanical interlocking of the lead frame.

In addition, the holes 602 serve to isolate and preserve rim/runway area606 (from the die to the edge of the die-pad) for down bonding. Inparticular the presence of the holes serves to contain unwanted bleedingor overflow of die attach material during the die attach step. Forexample, in one embodiment where the diepad has an overall width of 5.1mm, the hole may have a width of 0.2 mm, and may be separated from thediepad edge by a distance of 0.2 mm forming the down bond runway.

Lead frames according to embodiments of the present invention maycombine multiple features that are formed by coining. For example, thelead frame shown in FIGS. 6A-B features both the coined holes, and pinshaving elevated portions and cross-sectional profiles formed by coining.

As a further example of a lead frame having multiple coined features,FIG. 7A is a simplified cross-sectional view of another embodiment of alead frame of the present invention. FIG. 7B shows an enlarged plan viewof a portion of the lead frame of FIG. 7A including a supported die.FIG. 7C shows an enlarged cross-sectional view of the lead frame of FIG.7B taken along line C-C′, including a supported die.

Specifically, the lead frame 700 of the embodiments of FIGS. 7A-Cincludes both a coined indent 702 on the underside of the periphery ofthe diepad, and a plurality of holes 704 formed by coining in theperiphery of the diepad region. The location of holes 704 define a downbond runway region 706 that is configured to receive a down bond wirefrom the supported die, and which is shielded from overflow of dieattach material by the holes.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

1. A process of fabricating a package for a semiconductor device, themethod comprising: providing a metal layer; punching a pattern of holesthrough the metal layer to define a diepad and a plurality of pins;stamping a portion of the metal layer to: elevate a portion of a pinabove a horizontal plane of the diepad, and impart a pin with a complexcross-sectional profile that is other than square or rectangular; andencapsulating at least a portion of the elevated portion of the pin andcomplex cross-sectional profile within a package body.
 2. The process ofclaim 1 further comprising wherein the stamping forms an indent on aportion of the diepad or on a portion of a pin.
 3. The process of claim1 wherein the complex cross-sectional profile mechanically interlocksthe pin within the package body.
 4. The process of claim 1 wherein thecomplex cross-sectional profile is selected from chamfered,hourglass-shaped, T-shaped, I-shaped, concave, convex, or saw toothed.5. The process of claim 1 wherein the stamping creates a hole proximateto a periphery of the diepad.
 6. The process of claim 5 wherein a downbond runway region is defined between the hole and an edge of thediepad.
 7. The process of claim 1 wherein the punching creates theplurality of pins exhibiting a width of 0.15 mm or greater.
 8. Theprocess of claim 1 wherein the punching creates the plurality of pinshaving a pitch of 0.4 mm or greater.
 9. The process of claim 1 whereinproviding the metal layer comprises providing a copper roll.
 10. Theprocess of claim 9 wherein providing the copper roll comprises providinga copper roll having a thickness of between about 0.004-0.020″.
 11. Theprocess of claim 1 further comprising electroplating a portion of thepins.
 12. The process of claim 11 further comprising electroplating adie attach portion of the diepad.
 13. The process of claim 12 furthercomprising oxidizing the electroplated diepad to form a guard bandaround the die attach portion.
 14. The process of claim 1 furthercomprising attaching a die to the diepad with an electrically conductingadhesive material.
 15. The process of claim 14 wherein the electricallyconducting adhesive material is pre-coated on a backside of the die. 16.The process of claim 14 wherein the electrically conducting adhesivematerial is coated on the diepad prior to attachment of the die.
 17. Theprocess of claim 14 wherein a spreading of the electrically conductingadhesive material is contained by an oxide guard band.
 18. The processof claim 14 further comprising providing an electrically conducting clipbetween a contact on the die and a pin.
 19. The process of claim 1wherein the punching creates at least two pins integral with the diepadand with orthogonal portions of the surrounding metal roll.